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Lesson #42: How much silver?

Lesson #43: Salty Battery

Using ocean water (or make your own with salt and water), you can generate enough power to light up your LEDs, sound your buzzers, and turn a motor shaft. We’ll be testing out a number of different materials such as copper, aluminum, brass, iron, silver, zinc, and graphite to find out which works best for your solution.

The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.

When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.

Here’s what you need:

water
salt
vinegar (distilled white)
bleach IMPORTANT: WEAR GOGGLES!
glass container (like a cleaned out jam jar)
electrodes
real silverware (not stainless)
shiny nail (galvanized)
large paper clip
dull nail (iron)
wood screws (brass)
copper pennies minted before 1982 (or a short section of copper pipe)
graphite from inside a pencil (use a mechanical pencil refill)
2 alligator wires
digital multimeter

Download Student Worksheet & Exercises

Here’s what you do:

Fill a cup with water, adding a teaspoon of salt, a teaspoon of distilled white vinegar, and a few drops of bleach. NOTE: BE very careful with bleach! Cap it and store as soon as you’ve added it to the cup.
Find two of the following materials: copper*, aluminum*, brass, iron, silver, zinc, graphite (* indicates the ones that are easiest to start with – use a copper penny and a piece of aluminum foil). Attach an alligator clip lead to each one and dunk into your cup. Make sure these two metals DO NOT TOUCH in the solution.
You’ve just made a battery! Test it with your digital volt meter and make a note of the voltage reading. Connect the multimeter in series to read the current (remove a clip from the metal and clip it to one test probe, and attach the other test probe to the metal. Make sure you’re reading AMPS, not VOLTS when you note the reading for current).
Test out different combinations of materials and note which gives the highest voltage reading for you. Is it enough to light an LED? Buzzer? Motor? What if you made two of these and connected them in series? Three? Four?

Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.

Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.

You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.

Exercises

Which combination gives the highest voltage?
What happens if you use two strips of the same material?
What would happen if we used non-metal strips?

Lesson #44: Oxidation Numbers

Lesson #45: Redox Reaction

This experiment is for advanced students. We’re going to look at the strength of redox reactions using copper, zinc, and acids.

Materials:

shiny steel nails or zinc strip
calcuim chloride
copper sulfate
3 test tubes with stoppers
distilled water
distilled vinegar
safety goggles and gloves

Shine up your nails or zinc strip.
Create a solution of copper sulfate and water in a test tube and insert the nail and let it sit for a few minutes.
To a second test tube, add water and calcium chloride. Insert the shiny nail in to this test tube,
To the third test tube, insert distilled white vinegar and add a nail.
Look carefully at each test tube and compare your results with the original nail to see if the solution reacted with the nail.

We’re going to get zinc to react with different molecules in solution. You’re looking for a reaction that either changes the color of the nail, the solution, or forms tiny bubbles on the surface of the nail.

For the calcium carbonate, you’ll find tiny bubbles up and down the nail. The calcium ions are reduced and zinc ions are oxidized. For the copper sulfate, the nail changed color dramatically!

Lesson #46: Silverware Redox

Lesson #47: Silverware Battery

Never polish your tarnished silver-plated silverware again! Instead, set up a ‘silverware carwash’ where you earn a nickel for every piece you clean. (Just don’t let grandma in on your little secret!)

We’ll be using chemistry and electricity together (electrochemistry) to make a battery that reverses the chemical reaction that puts tarnish on grandma’s good silver. It’s safe, simple, and just needs a grown-up to help with the stove.

Here’s what you need:

stove (with adult help)
skillet
aluminum foil
water
baking soda
salt
real silverware (not stainless)

Download Student Worksheet & Exercises

You can safely dip it into a self-polishing solution:

In a saucepan lined with aluminum foil, heat a solution of 1 cup water, 1 teaspoon baking soda, and 1 teaspoon salt.
When your solution bubbles, place the tarnished silverware directly on the foil. (Try a piece that’s really tarnished to see the cleaning effects the best.)

What’s happening? This is a very simple battery, believe it or not! The foil is the negative charge, the silverware is the positive, and the water-salt-baking-soda solution is the electrolyte.

Your silver turns black because of the presence of sulfur in food. Here’s how the cleaning works: The tarnished fork (silver sulfide) combines with some of the chemicals in the water solution to break apart into sulfur (which gets deposited on the foil) and silver (which goes back onto the fork). Using electricity, you’ve just relocated the tarnish from the fork to the foil. Just rinse clean and wipe dry.

Toss the foil in the trash (or recycling) when you’re done, and the liquids go down the drain.

Exercises

Where is the electrolyte in this experiment?
Where does the black stuff that was originally on the silverware go?
Where’s the electricity in this experiment?
Where would you place your DMM probes to measure the generated voltage?

Lesson #48: Thermochemistry

Lesson #49: Thermometers

First invented in the 1600s, thermometers measure temperature using a sensor (the bulb tip) and a scale. Temperature is a way of talking about, measuring, and comparing the thermal energy of objects. We use three different kinds of scales to measure temperature. Fahrenheit, Celsius, and Kelvin. (The fourth, Rankine, which is the absolute scale for Fahrenheit, is the one you’ll learn about in college.)

Mr. Fahrenheit, way back when (18th century) created a scale using a mercury thermometer to measure temperature. He marked 0° as the temperature ice melts in a tub of salt. (Ice melts at lower temperatures when it sits in salt. This is why we salt our driveways to get rid of ice). To standardize the higher point of his scale, he used the body temperature of his wife, 96°.

As you can tell, this wasn’t the most precise or useful measuring device. I can just imagine Mr. Fahrenheit, “Hmmm, something cold…something cold. I got it! Ice in salt. Good, okay there’s zero, excellent. Now, for something hot. Ummm, my wife! She always feels warm. Perfect, 96°. ” I hope he never tried to make a thermometer when she had a fever.

Just kidding, I’m sure he was very precise and careful, but it does seem kind of weird. Over time, the scale was made more precise and today body temperature is usually around 98.6°F.

Later, (still 18th century) Mr. Celsius came along and created his scale. He decided that he was going to use water as his standard. He chose the temperature that water freezes at as his 0° mark. He chose the temperature that water boils at as his 100° mark. From there, he put in 100 evenly spaced lines and a thermometer was born.

Last but not least Mr. Kelvin came along and wanted to create another scale. He said, I want my zero to be ZERO! So he chose absolute zero to be the zero on his scale.

Absolute zero is the theoretical temperature where molecules and atoms stop moving. They do not vibrate, jiggle or anything at absolute zero. In Celsius, absolute zero is -273 ° C. In Fahrenheit, absolute zero is -459°F (or 0°R). It doesn’t get colder than that!

As you can see, creating the temperature scales was really rather arbitrary:

“I think 0° is when water freezes with salt.”
“I think it’s just when water freezes.”
“Oh, yea, well I think it’s when atoms stop!”

Many of our measuring systems started rather arbitrarily and then, due to standardization over time, became the systems we use today. So that’s how temperature is measured, but what is temperature measuring?

Temperature is measuring thermal energy which is how fast the molecules in something are vibrating and moving. The higher the temperature something has, the faster the molecules are moving. Water at 34°F has molecules moving much more slowly than water at 150°F. Temperature is really a molecular speedometer.

Let’s make a quick thermometer so you can see how a thermometer actually works:

Materials:

plastic bottle
straw
hot glue or clay
water
food coloring
rubbing alcohol
index card and pen

When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!

Lesson #50: Thermal Energy

Lesson #51: Football Ice Cream

Is it hot where you live in the summer? What if I gave you a recipe for making ice cream that doesn’t require an expensive ice cream maker, hours of churning, and can be made to any flavor you can dream up? (Even dairy-free if needed?)

If you’ve got a backyard full of busy kids that seem to constantly be in motion, then this is the project for you. The best part is, you don’t have to do any of the churning work… the kids will handle it all for you!

This experiment is simple to set up (it only requires a trip to the grocery store), quick to implement, and all you need to do guard the back door armed with a hose to douse the kids before they tramp back into the house afterward.

One of the secrets to making great ice cream quickly is to be sure that the milk and cream is COLD. I will make this particular recipe, it’s usually with hundreds of kids, and our staff will stuff the milk products in the freezer for an hour or two or under hundreds of pounds of ice to make sure it’s super-cold.

If you’re going for the dairy-free kind, simply skip the milk and cream and add a bit of extra time to the chill time of your substitute ‘milk’. We’ve had the best luck with almond and soy milk. Are you ready?

Here’s what you need:

Materials:

1 quart whole milk (do not substitute, unless your child has a milk allergy, then use soy or almond milk)
1 pint heavy cream (do not substitute, unless your child has a milk allergy, then skip)
1 cup sugar (or other sweetener)
1 tsp vanilla (use non-alcohol kind)
rock salt (use table salt if you can’t find it)
lots of ice
freezer-grade zipper-style bags (you’ll need quart and gallon sizes)

Download Student Worksheet & Exercises

How does that work? Ice cream is basically “fluffy milk”. You need to whip in a lot of air into the milk fat to get the fluffy pockets that make this stuff worthwhile. The more the kids shake the bag, the faster it will turn into ice cream.

Why do we put salt on the ice?

If you live in an area where they put salt on the roads, you already know that people do this to melt the ice. But how does salt melt ice? Think about the chemistry of what’s going on. Water normally freezes at zero degrees Celsius. But salt water presses lower than zero, so the freezing point of salt water is lower than fresh water. By sprinkling salt on the roads, you’re lowering the point at which water freezes at. When you add a solute (salt) to the solvent (water) to alter the freezing point of the solution, it’s known as the “freezing point depression”.

Tips: Don’t use nonfat milk – it won’t work with this style of ice-cream making. if you’re adding fruit or chocolate bits, make sure you get those cold in advance too, or they will slow down your process as they heat your milk solution. (We usually add those bits last after the ice cream is done.)

IMPORTANT: Do NOT substitute dry ice for the water ice – the carbon dioxide gases build quickly and explode the bag, and now you have flying bits of dry ice that will burn skin upon contact. That’s not the biggest issue, though… the real problem is that now animals (like your dog) and small children pop a random piece of dry ice into their mouths, which will earn your family a visit to the ER. So stick with the regular ice from your fridge.

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